1. Field of the Invention
The present invention relates to a system for monitoring of the level of fuel for a dwelling's heating unit wherein the level is displayed remotely at a thermostat in the dwelling.
2. The State of the Art
Dwelling units typically are heated using as energy sources one or more of gas, oil, or electricity. Energy sources with fuel stored locally at the dwelling include oil and other liquid fuels (e.g., propane); natural gas and electricity are typically available from a distributed system and so are not stored locally at the dwelling unit.
Especially in the Northeast United States, a significant number of homes are heated with oil. The oil is generally stored in a tank adjacent to the dwelling unit, and a pump associated with the tank pumps the oil to a heating unit within the dwelling. The occupant of the dwelling, or an oil delivery service, periodically must check the oil level in the tank and, if necessary, order more oil from an oil delivery service if the tank is running low. In domestic oil tanks, the level is typically measured using either a dipstick or a simple flotation device (described below and generally shown in FIG. 2).
There are quite a number of patented and commercialized devices for determining, sometimes remotely, the level of liquid in a tank, some of which are now described. Krehel et al. (U.S. Pat. No. 4,524,617) describe a fuel gauge for a propane tank, such as used with a portable gas grill for cooking, comprising a scale that weighs the tank and thereby estimates the amount of fuel remaining therein. Parker (U.S. Pat. No. 5,323,652) describes a level indicator comprising a thermochromic strip that senses and displays (through a thermochromic material) the temperature difference on the outside of the tank resulting from the cooling effect of liquid propane adjacent the strip. Koon (U.S. Pat. No. 5,005,407) describes a level indicator for a tank including a sensing strip attached to a power source to cause the strip to generate an electrostatic filed that changes proportionally to the level in the tank; the sensed level can be displayed remotely. Stinson (U.S. Pat. No. 4,480,610) describes a remote oil level indicator, especially for sensing a low level in a fuel tank for an internal combustion engine (e.g., for an automobile) by sensing the pressure change in a closed tubular conduit disposed in the tank below the fuel level line. Clarkson (U.S. Pat. No. 4,459,584) discloses an automatic liquid level indicator and alarm system utilizing a float connected to a line having magnets thereon and the position of the magnets is sensed to determine the level of liquid in the tank. The disclosures of all of these patents are incorporated herein by reference. Various other level indicators and switching devices are manufactured and/or sold by such entities as IMO Industries, Inc. (Gem Sensors Div., Plainville, Conn.), Advanced Control Technology, Inc. (Bloomington, Minn.), KIP Incorporated (Farmington, Conn.), and Madison Co. (Branford, Conn.); radar level gauges (available from Endress+Hauser, Greenwood, Ind.), akin to sensors for focussing automatic cameras, are also suitable. Various thermostat manufacturers including Honeywell Corp. (Home and Building Control Div., Golden Valley, Minn.), Hunter Fan Co. (Memphis, Tenn.), Emerson Elec. Co. (White Rogers Div., St. Louis, Mo.), and Robertshaw Control Co. (Long Beach, Calif.).
The unappreciated problem yet to be addressed by any of these patents and manufacturing/sales entities is an easy way to remotely sense the level of fuel in the tank and to display that information in a useful and convenient manner to the occupant of the dwelling. At present, as noted above, the occupant (or the oil delivery service) must periodically monitor the oil level in the tank to assure a timely order for more fuel oil and avoid freezing the pipes. For the elderly, and in bad weather, it may be very difficult to ascertain the level of fuel in the tank, so that the possibility of running out of heating fuel becomes a real possibility. When the fuel tank is outside or in a basement, a disabled or handicapped individual (e.g., one requiring crutches or a wheelchair, or otherwise unable to traverse stairs) may not physically be able to check the level of the fuel tank, thus requiring reliance on another person to periodically check the tank level.